Electromagnetic valve control apparatus and control method thereof

ABSTRACT

A control apparatus of an electromagnetic valve which includes a valve element, an armature connected to an armature shaft which is engaged with the valve element, a pair of spring means for energizing the valve element toward the valve-opening side and the valve-closing side, respectively, and an electromagnet for energizing the armature toward the valve-closing side of the valve element, and which operates the valve element to open and close by cooperative operation of an electromagnetic force of the electromagnet and an energizing force of the spring means, is provided with a controller which increases the energizing force of the spring means for energizing the valve element toward the valve-closing side immediately before seating of the valve element. By this type of the control apparatus of the electromagnetic valve, an increase in power consumption of the electromagnetic valve is suppressed.

INCORPORATION BY REFERENCE

[0001] The disclosure of Japanese Patent Application No. 2002-118806filed on Apr. 22, 2002, including the specification, drawings andabstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a control apparatus of anelectromagnetic valve for operating a valve element to open and close byan electromagnetic force of an electromagnet and an energizing force ofa spring, and a control method of the same.

[0004] 2. Description of Related Art

[0005]FIG. 10a shows an example of a configuration of the aforementionedtype of the electromagnetic valve. In this electromagnetic valve, acylinder 140 is formed in a cylinder head 110 of an internal combustionengine, and an upper end of an opening of the cylinder 140 is coveredwith an electromagnet (valve-opening electromagnet) 139 for energizing avalve element 121 which functions as an intake and exhaust valve of theengine. In addition, a valve-closing air spring (pneumatic spring) 146and a valve-opening air spring (pneumatic spring) 148 are formed in thecylinder 140. In this case, the valve-closing air spring 146 is disposedagainst the bottom face of the cylinder 140, and is provided with apiston 141 connected to a valve shaft 122 of the valve element 121.Furthermore, the structure is such that the compressed air within apressure chamber 145 defined by the piston 141, cylinder 140, and thebottom face thereof applies to the piston 141 an energizing force in adirection for closing the valve element 121. Meanwhile, thevalve-opening air spring 148 is disposed against the opening face of thecylinder 140, that is, the bottom face of the valve-openingelectromagnet 139, and is provided with a piston 142 connected to asupporting shaft (armature shaft 123) of an armature 124 on which theelectromagnetic force of the valve-opening electromagnet 139 acts.Furthermore, the structure is such that the compressed air within apressure chamber 147 defined by the piston 141, cylinder 140, and thebottom face of the valve-opening electromagnet 139 which covers theopening face of the cylinder 140 applies to the piston 142 theenergizing force in a direction for opening the valve element 121.

[0006] Moreover, the armature shaft 123 connected to the piston 142 ofthe valve-opening air spring 148 and the valve shaft 122 connected tothe piston 142 of the valve-closing air spring 146 are connected totheir corresponding pistons 141 and 141 in such a manner as to passthrough and protrude from the pistons, such that the armature shaft 123and the valve shaft 122 oppose with each other. Accordingly, a tappetfor transmitting power is constituted by the armature shaft 123 and thevalve shaft 122 which protrude and oppose with each other.

[0007] On the other hand, at a position opposing the valve-openingelectromagnet 139 which covers the cylinder 140, an electromagnet(valve-closing electromagnet) 135 for energizing the valve element 121in the valve closing direction is disposed with the armature 124provided between the electromagnet 139 and the electromagnet 135. Bycooperative operation of the electromagnetic force of the valve-closingelectromagnet 135 and the valve-opening electromagnet 139 and thevalve-closing air spring 146 and the valve-opening air spring 148, thevalve element 121 is operated to open and close against a valve seat 111provided in the cylinder head 110.

[0008] Meanwhile, with respect to such electromagnetic valve having theair springs as mentioned above, if a speed (contact speed) at which thearmature 124 contacts the valve-closing electromagnet 135 and thevalve-opening electromagnet 139 is high, a problem such as a loudcontact noise may arise. Therefore, conventionally, as indicated in theJapanese Patent laid-Open Publication No. 2000-27616 for example, it hasbeen suggested that the elastic force of the valve-closing air spring146 is increased in the vicinity of a full-open position of the valveelement 121 during valve opening operation, whereas the elastic force ofthe valve-opening air spring 148 is increased in the vicinity of thefull-close position of the valve element 121 during valve closingoperation. This may relieve the impact upon contact of the armature 124against the valve-closing electromagnet 135 or the valve-openingelectromagnet 139, thereby allowing to lessen the contact noise involvedwith such contact operation.

[0009] According to the electromagnetic valve described in theaforementioned publication, the contact noise generated when thearmature 124 contacts the valve-closing electromagnet 135 and thevalve-opening electromagnet 139 can certainly be reduced. However,particularly during opening of the valve element 121, the followinginconvenience also occurs when the armature 124 is attracted to thevalve-opening electromagnet 135.

[0010] That is, since the tappet between the valve shaft 122 and thearmature shaft 123 is normally provided with a predetermined clearance,after the valve element 121 is seated on the valve seat 111, thearmature shaft 123 separates from the valve shaft 122 and the armature124 continues to be further attracted by the valve-closing electromagnet135. Meanwhile, after the valve element 121 is seated on the valve seat111, the energizing force of the valve-closing air spring 146 toward thevalve-closing side is not applied to the armature 124, in correlationwith the separation of the armature shaft 123. Therefore, in order tocertainly attract (attach) the armature 124 to the valve-closingelectromagnet 135, in a manner shown in FIG. 10b, against the energizingforce of the valve-opening air spring 148 toward the valve-opening side,the amount of power supplied to the valve-closing electromagnet 135 mustbe increased. Moreover, the electromagnetic force by which thevalve-closing electromagnet 135 attracts the armature 124 suddenlyincreases as a gap between the valve-closing electromagnet 135 and thearmature 124 becomes small. As a result, a speed at which the armature124 contact the valve-closing electromagnet 135 increases, thereby alsoincreasing the contact noise involved with such contact operation.

SUMMARY OF THE INVENTION

[0011] The invention has been made in view of the aforementionedconditions, and it is an object of the invention to provide a controlapparatus of an electromagnetic valve by which an armature connected toan armature shaft which transmits power in relation to the valve shaftcan be certainly attracted to an electromagnet which attracts thearmature in the valve-closing direction of a valve element, whilesuppressing an increase in power consumption and the like.

[0012] Therefore, according to an exemplary embodiment, with respect toan electromagnetic valve which includes a valve element, an armatureconnected to an armature shaft which engages with the valve element, apair of spring means for energizing the valve element toward avalve-opening side and a valve-closing side, respectively, and anelectromagnet for energizing the armature toward the valve-closing sideof the valve element, and which operates the valve element to open andclose by cooperative operation of an electromagnetic force of theelectromagnet and an energizing force of the spring means, a controlapparatus is provided that is equipped with a controller for increasing,immediately before the valve element is seated, the energizing force ofthe spring means which energizes the valve element toward thevalve-closing side.

[0013] Furthermore, according to an exemplary embodiment, a controlmethod of a control apparatus of an electromagnetic valve which includesa valve element, an armature connected to an armature shaft whichengages with the valve element, a pair of spring means for energizingthe valve element toward a valve-opening side and a valve-closing side,respectively, and an electromagnet for energizing the armature towardthe valve-closing side of the valve element, and which operates thevalve element to open and close by cooperative operation of anelectromagnetic force of the electromagnet and an energizing force ofthe spring means, comprises the following steps of:

[0014] supplying an electric current to the electromagnet so as toenergize the valve element toward the valve-closing side; and

[0015] increasing, immediately before seating of the valve element, theenergizing force of the spring means which energizes the valve elementtoward the valve-closing side.

[0016] According to the control apparatus of the electromagnetic valveand the control method thereof as described above, the energizing forceof the spring means for energizing the valve element toward thevalve-closing side is increased immediately before seating of the valveelement. Therefore, compared to a case where the energizing force is notincreased, the energizing force for energizing the armature toward thevalve-opening side by a resultant force of a pair of spring means isreduced. In addition, if the amount of increase in the energizing forceis large, displacement of the armature toward the valve-closing side isaccelerated. Accordingly, the degree of decrease in the inertia force ofthe armature due to the energizing force for energizing the armaturetoward the valve-opening side by the resultant force of the pair ofspring means is reduced immediately before the valve element is seated.Furthermore, if the amount of increase in the energizing force of thespring means for energizing the valve element toward the valve-closingside is large, the inertia force of the armature increases.Consequently, the armature can certainly be attracted to theelectromagnet which energizes (attracts) the armature in thevalve-closing direction of the valve element while suppressing anincrease in power consumption and the like.

[0017] Furthermore, according to an exemplary embodiment, according toan exemplary embodiment, with respect to an electromagnetic valve whichincludes a valve element, an armature connected to an armature shaftwhich engages with the valve element, a pair of spring means forenergizing the valve element toward a valve-opening side and avalve-closing side, respectively, and an electromagnet for energizingthe armature toward the valve-closing side of the valve element, andwhich operates the valve element to open and close by cooperativeoperation of an electromagnetic force of the electromagnet and anenergizing force of the spring means, a control apparatus is providedthat is equipped with a controller for reducing, immediately before thevalve element is seated, the energizing force of the spring means whichenergizes the valve element toward the valve-opening side.

[0018] Furthermore, according to an exemplary embodiment, a controlmethod of a control apparatus of an electromagnetic valve which includesa valve element, an armature connected to an armature shaft whichengages with the valve element, a pair of spring means for energizingthe valve element toward a valve-opening side and a valve-closing side,respectively, and an electromagnet for energizing the armature towardthe valve-closing side of the valve element, and which operates thevalve element to open and close by cooperative operation of anelectromagnetic force of the electromagnet and an energizing force ofthe spring means, comprises the following steps of:

[0019] supplying an electric current to the electromagnet so as toenergize the valve element toward the valve-closing side; and

[0020] reducing, immediately before seating of the valve element, theenergizing force of the spring means which energizes the valve elementtoward the valve-opening side.

[0021] According to the control apparatus of the electromagnetic valveand the control method thereof as described above, the energizing forceof the spring means for energizing the valve element toward thevalve-opening side is reduced immediately before seating of the valveelement. Therefore, compared to a case where the energizing force is notreduced, the energizing force for energizing the armature toward thevalve-opening side by a resultant force of a pair of spring means isreduced. In addition, if the amount of decrease in the energizing forceof the spring means for energizing the valve element toward thevalve-opening side is large, displacement of the armature toward thevalve-closing side is accelerated. Accordingly, the degree of decreasein the inertia force of the armature due to the energizing force forenergizing the armature toward the valve-opening side by the resultantforce of the pair of spring means is reduced immediately before thevalve element is seated. Furthermore, if the amount of decrease in theenergizing force of the spring means for energizing the valve elementtoward the valve-opening side is large, the inertia force of thearmature increases. Consequently, the armature can certainly beattracted to the electromagnet which energizes (attracts) the armaturein the valve-closing direction of the valve element while suppressing anincrease in power consumption and the like.

[0022] Moreover, according to an exemplary embodiment, with respect toan electromagnetic valve which includes a valve element, an armatureconnected to an armature shaft which engages with the valve element, avalve-opening air spring for energizing the valve element toward avalve-opening side, a valve-closing air spring for energizing the valveelement toward a valve-closing side, and a pair of electromagnets forenergizing the armature in both axial directions of the armature shaft,and which operates the valve element to open and close by cooperativeoperation of an electromagnetic force of each electromagnet and anenergizing force of each air spring, a control apparatus is providedthat is equipped with a controller for forcibly reducing, immediatelybefore the valve element is seated, the degree of increase in theenergizing force by which the valve-opening air spring and thevalve-closing air spring energize the valve element toward thevalve-opening side in accordance with displacement of the valve elementtoward the valve-closing side.

[0023] Furthermore, according to yet another exemplary embodiment, acontrol method of a control apparatus of an electromagnetic valve whichincludes a valve element, an armature connected to an armature shaftwhich engages with the valve element, a valve-opening air spring forenergizing the valve element toward a valve-opening side, avalve-closing air spring for energizing the valve element toward avalve-closing side, and a pair of electromagnets for energizing thearmature in both axial directions of the armature shaft, and whichoperates the valve element to open and close by cooperative operation ofan electromagnetic force of each electromagnet and an energizing forceof each air spring, comprises the following steps of:

[0024] supplying an electric current to the electromagnet so as toenergize the valve element toward the valve-closing side; and

[0025] forcibly reducing, immediately before seating of the valveelement, the degree of increase in the energizing force by which thevalve-opening air spring and the valve-closing air spring energize thevalve element toward the valve-opening side in accordance withdisplacement of the valve element toward the valve-closing side.

[0026] Immediately before the valve element is seated, the inertia forceof the armature is reduced by the energizing force which energizes thearmature toward the valve-opening side by the resultant force of thevalve-opening air spring and the valve-closing air spring.

[0027] In this case, according to the control apparatus of theelectromagnetic valve and the control method thereof as described above,the degree of increase in the energizing force by which thevalve-opening air spring and the valve-closing air spring energize thevalve element toward the valve-opening side in accordance withdisplacement of the valve element toward the valve-closing side isforcibly reduced immediately before seating of the valve element.Accordingly, the degree of decrease in the inertia force of the armaturedue to the energizing force for energizing the armature toward thevalve-opening side by the resultant force of the valve-opening airspring and the valve-closing air spring is reduced immediately beforeseating of the valve element. Consequently, the armature can certainlybe attracted to the electromagnet which energizes (attracts) thearmature in the valve-closing direction of the valve element whilesuppressing an increase in power consumption and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above mentioned embodiment and other embodiments, objects,features, advantages, technical and industrial significances of thisinvention will be better understood by reading the following detaileddescription of the exemplary embodiments of the invention, whenconsidered in connection with the accompanying drawings, in which:

[0029]FIG. 1 is a drawing of a first exemplary embodiment of a controlapparatus of an electromagnetic valve according to the invention;

[0030]FIGS. 2a, 2 b, and 2 c are cross-sectional views whichschematically show operation modes of an air spring according to theexemplary embodiment;

[0031]FIG. 3 is a drawing which shows a relationship between a liftposition of a valve element and a pressure of the air spring accordingto the exemplary embodiment;

[0032]FIG. 4 is a drawing which shows a valve-closed state of the valveelement according to the exemplary embodiment;

[0033]FIG. 5 is a drawing which shows a valve-open state of the valveelement according to the exemplary embodiment;

[0034]FIG. 6 is a drawing which shows a state immediately before seatingof the valve element according to the exemplary embodiment;

[0035]FIGS. 7a and 7 b are drawings which show control modes of the airspring according to the exemplary embodiment;

[0036]FIG. 8 is a drawing which show a state in which an armature isseated according to the exemplary embodiment;

[0037]FIG. 9 is a drawing which shows a control mode immediately beforeseating of the valve element according to a second exemplary embodimentof the control apparatus of the electromagnetic valve of the invention;and

[0038]FIGS. 10a and 10 b are drawings which show control modes of aconventional electromagnetic valve.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0039] In the following description and the accompanying drawings, theinvention will be described in more detail in terms of exemplaryembodiments.

[0040] (First Exemplary Embodiment)

[0041] A control apparatus of an electromagnetic valve according to afirst exemplary embodiment will be described at first. Each of an intakevalve and exhaust valve of an internal combustion engine is configuredas an electromagnetic valve which is opened and closed by cooperativeoperation of an electromagnetic force of an electromagnet and an elasticforce (energizing force) of a pair of air springs. More specifically,the electromagnetic valve is equipped with a pair of electromagnets forenergizing an armature connected to an armature shaft in both armatureaxial directions. Furthermore, the electromagnetic valve includes avalve-opening air spring for energizing a piston connected to thearmature shaft toward the valve-opening side of a valve element by apressure in a pressure chamber, and a valve-closing air spring forenergizing a piston connected to a valve shaft which is an axis of thevalve element toward the valve-closing side of the valve element by apressure in a pressure chamber. The valve element is operated to openand close by cooperative operation of the electromagnetic force whichacts on the armature by the pair of electromagnets and the energizingforce of the pair of air springs. Since the intake valve and the exhaustvalve have the same basic structure, the intake valve is taken as anexample herein to describe its internal structure.

[0042] A cylinder head 10 of an internal combustion engine shown in FIG.1 is formed with an intake port 12 which is connected to a combustionchamber 11, and is provided with an electromagnetic valve 20 for openingand closing the intake port 12.

[0043] The electromagnetic valve 20 generally includes a valve element21 provided at one end of a valve shaft 22, an electromagnetic driveportion 30 which generates an electromagnetic force for opening andclosing the valve element 21, and a pair of air springs 46 and 48 whichenergize the valve element 21 toward a valve-closing side displacementend and a valve-opening side displacement end, respectively.

[0044] The valve element 21 is arranged in an opening of the intake port12 in such a manner as to be exposed to the inside of the combustionchamber 11. A valve seat 13 is provided at the outer edge of the openingof the intake port 12. The intake port 12 is opened and closed as thevalve element 21 is separated from or seated on the valve seat 13. Thatis, as the valve element 21 is displaced upward in FIG. 1 to be seatedon the valve seat 13, the intake port 12 is closed with respect to thecombustion chamber 11. Furthermore, as the valve element 21 seated onthe valve seat 13 is displaced downward in FIG. 1 to be separated fromthe valve seat 13, the intake port 12 is opened with respect to thecombustion chamber 11.

[0045] The valve shaft 22 whose one end is provided with the valveelement 21 is supported by a valve guide 14 fixed to the cylinder head10 in such a manner as to allow reciprocating motion in an axialdirection. The upper end of the valve shaft 22 is placed in contact withthe lower end of an armature shaft 23. The armature shaft 23 issupported by an armature guide 15 fixed to the cylinder head 10 in sucha manner as to allow reciprocating motion coaxially with the valve shaft22.

[0046] On the upper end of the armature shaft 23, an armature 24 that ismade of high permeable material and generally formed in a disc shape isfixed. Furthermore, the upper portion of the armature shaft 23 on whichthe armature 24 is fixed is housed within a casing 31 of theelectromagnetic drive portion 30.

[0047] In the casing 31, an upper core 32 made of high permeablematerial is fixed above the armature 24. An annular groove 33 is formedon a face of the upper core 32 that faces the armature 24, and acylindrically-wound electromagnetic coil 34 is housed within the groove33. The upper core 32 and the electromagnetic coil 34 constitute avalve-closing electromagnet 35 for operating the valve element 21 in avalve-closing direction.

[0048] On the other hand, under the armature 24 in the casing 31, alower core 36 also made of high permeable material is fixed at apredetermined distance from the upper core 32. Also on the lower core36, an annular groove 37 is formed on a face that faces the armature 24,and a cylindrically-wound electromagnetic coil 38 is housed within thegroove 37. The lower core 36 and the electromagnetic coil 38 constitutea valve-opening electromagnet 39 for operating the valve element 21 in avalve-opening direction.

[0049] Furthermore, in the casing 31, a displacement sensor 70 isprovided for detecting displacement of the armature 24. A lift positionof the valve element 21 can be confirmed based on a detection result ofthe displacement sensor 70.

[0050] Meanwhile, in the cylinder head 10, a cylinder 40 with an opencircular shape is formed between the valve guide 14 and the armatureguide 15. Furthermore, a generally disc shaped piston 42 is fixed to thevalve shaft 22, and also a generally disc shaped piston 42 is fixed tothe armature shaft 23. These pistons 41 and 42 are disposed in such amanner allowing reciprocating motion in an axial direction of the valveshaft 22 and the armature shaft 23 while being slidably in contact witha side wall of the cylinder 40.

[0051] Inside the cylinder 40 is divided into three spaces by the piston41 and the piston 42. Of these three spaces, a middle space 43 formedbetween the piston 41 and the piston 42 is open to the outside via acommunicating passage 44. Furthermore, a valve-closing air spring 46 anda valve-opening air spring 48 are constituted with the space 43 providedtherebetween.

[0052] That is, the valve-closing air spring 46 is constituted of thepiston 41 and a portion of the cylinder 40 on the valve guide 14 side.In this case, within the cylinder 40, a space 45 formed between thevalve guide 14 and the piston 41 fixed to the valve shaft 22 is suppliedwith compressed air via an air supply passage 50, and the compressed airwithin the space 45 is discharged through an exhaust passage 51. In thiscase, the space 45, the air supply passage 50, and the exhaust passage51 constitute a pressure chamber of the valve-closing air spring 46. Theair pressure within the pressure chamber (more accurately, a pressuredifference between the air pressure within the pressure chamber and thatwithin the space 43, or the atmospheric pressure) energizes the valveshaft 22 toward the valve-closing side (upward in FIG. 1) of the valveelement 21 via the piston 41.

[0053] Furthermore, the valve-opening air spring 48 is constituted ofthe piston 42 and a portion of the cylinder 40 on the armature guide 15side. In this case, within the cylinder 40, a space 47 formed betweenthe armature guide 15 and the piston 42 fixed to the armature shaft 23is supplied with compressed air via an air supply passage 52, and thecompressed air within the space 47 is discharged through an exhaustpassage 53. In this case, the space 47, the air supply passage 52, andthe exhaust passage 53 constitute a pressure chamber of thevalve-opening air spring 48. The air pressure within the pressurechamber (more accurately, a pressure difference between the air pressurewithin the pressure chamber and that within the space 43, or theatmospheric pressure) energizes the armature shaft 23 toward thevalve-opening side (downward in FIG. 1) of the valve element 21 via thepiston 42.

[0054] Next, a structure of an air pressure circuit for thevalve-closing air spring 46 and the valve-opening air spring 48 will bedescribed with reference to FIG. 1. The air pressure circuit is providedwith an air pump 60 and a reservoir tank 62.

[0055] The air pump 60 compresses air taken in from outside and suppliesthe compressed air to the reservoir tank 62 via a throttle 61. Thecompressed air supplied from the air pump 60 is accumulated in thereservoir tank 62. A pressure of the compressed air accumulated in thereservoir tank 62 is maintained constant by a regulator or the like (notshown).

[0056] The reservoir tank 62 is connected to the pressure chamber of thevalve-closing air spring 46 via a supply passage 63. Furthermore, thereservoir tank 62 is connected to the pressure chamber of thevalve-opening air spring 48 via a supply passage 64.

[0057] More specifically, the supply passage 63 is connected to the airsupply passage 50 via a non-return valve 65. Furthermore, the supplypassage 64 is connected to the air supply passage 52 via a non-returnvalve 66.

[0058] The non-return valves 65 and 66 are differential pressureoperating valves of normally closed type, and open when the pressureswithin the pressure chambers of the valve-closing air spring 46 and thevalve-opening air spring 48 become lower than the pressures of thesupply passages 63 and 64, so as to supply compressed air to thepressure chambers.

[0059] Moreover, the exhaust passage 51 of the valve-closing air spring46 and the exhaust passage 53 of the valve-opening air spring 48 areprovided with a relief valves 67 and 68, respectively. The relief valves67 and 68 normally function as pressure operating valves of normallyclosed type which open when the air pressure of the exhaust passages 51and 53 has become equal to or higher than a predetermined level, so asto discharge extra compressed air from the pressure chamber.Furthermore, the relief valves 67 and 68 are also structured so as to beforcibly opened or closed by a command from outside. The downstream ofthe relief valves 67 and 68 is open to the air.

[0060] The amount of compressed air filled within the pressure chambersof the valve-closing air spring 46 and the valve-opening air spring 48is regulated through the non-return valves 65 and 66, the relief valves67 and 68, and the like, so as to obtain a desired elastic force.

[0061] Although not shown in FIG. 1, each of intake valve and exhaustvalve of the internal combustion chamber is provided with the non-returnvalves 65 and 66, the relief valves 67 and 68, and the supply passages63 and 64. According to this structure, the air pressure of the airspring provided for each intake valve and exhaust valve of the internalcombustion engine can also be adjusted individually.

[0062] Next, the structure of a control system of the electromagneticvalve 20 described above will be explained with reference to FIG. 1.

[0063] To an input port of an electronic control unit (ECU) 71 whichexecutes various controls of the internal combustion engine, detectionsignals of various sensors, such as a crank angle sensor and anaccelerator sensor, that detect an operation state of the engine, inaddition to a detection signal of the displacement sensor 70 are input.Furthermore, an electromagnetic coil driving circuit 72 is connected toan output port of the electronic control unit 71.

[0064] The electronic control unit 71 generates a control signal forsupplying power to both electromagnetic coils 34 and 38 on the basis ofthe engine operation state identified based on the detection signals ofeach sensor mentioned above, and outputs the control signal to theelectromagnetic coil driving circuit 72. The electromagnetic coildriving circuit 72 amplifies the control signal to generate anelectromagnetic coil driving current, and supplies power to each of theelectromagnetic coils 34 and 38.

[0065] Furthermore, the electronic control unit 71 controls the reliefvalves 67 and 68 so as to adjust the air pressure within the pressurechambers of the valve-closing air spring 46 and the valve-opening airspring 48 according to the engine operation state.

[0066] In the electromagnetic valve 20 as structured as above accordingto the exemplary embodiment, the valve element 21 which is displacedalong with the valve shaft 22 and the armature shaft 23 is capable ofreciprocating between a position at which the valve element 21 seats onthe valve seat 13 and a position at which the armature 24 contacts thelower core 36.

[0067] In this case, at a lift position of the valve element 21 at whichthe valve element is seated on the valve seat 13, that is, at thevalve-closing side displacement end of the valve element 21, theelectromagnetic valve 20 is fully closed. The lift position of the valveelement 21 in this state is called a “full-close position.”

[0068] Furthermore, at a lift position of the valve element 21 at whichthe armature 24 contacts the lower core 36, that is, at thevalve-opening side displacement end of the valve element 21, the valveelement 21 is kept apart from the valve seat 13 to the maximum, and thusthe electromagnetic valve 20 is fully opened. The lift position of thevalve element 21 in this state is called a “full-open position.”

[0069] In the electromagnetic valve 20, when no electromagnetic force isgenerated by the electromagnets 35 and 39, the valve element 21 which isdisplaced along with the valve shaft 22 and the armature shaft 23 isplaced at a position at which an elastic force Fcl of the valve-closingair spring 46 and an elastic force Fop of the valve-opening air spring48 are equal. Herein, a lift position of the valve element 21 at whichthe elastic force Fcl of the valve-closing air spring 46 and the elasticforce Fop of the valve-opening air spring 48 are balanced is called a“neutral position.”

[0070] In addition, when the elastic forces of the valve-closing airspring 46 and the valve-opening air spring 48 are equal, and theexternal environments of both springs are the same, the air pressure inthe valve-closing air spring 46 and that in the valve-opening air spring48 assume the same pressure Pn, as shown in FIG. 2b. In this exemplaryembodiment, on the basis of a position (reference position) at which theelastic forces of the valve-closing air spring 46 and the valve-openingair spring 48 become equal under the same external environments, forces(elastic forces) applied to pressure-receiving surfaces of the pistons41 and 42 in accordance with displacement of the pistons are set to beequal with each other. This can be achieved by equalizing, at theaforementioned reference position, the capacities of the pressurechambers of the valve-closing air spring 46 and the valve-opening airspring 48, and the pressure-receiving areas of the pistons 41 and 42.

[0071] As the valve element 21 is displaced from the neutral position,the pistons 41 and 42 are also displaced within the cylinder 40, andaccordingly the capacity of each pressure chamber of the valve-closingair spring 46 and the valve-opening air spring 48 changes, therebycausing the air pressure therein to change. FIG. 3 illustrates a patternof such air pressure change within the pressure chamber based on thelift position of the valve element 21.

[0072] After being minimized at the full-open position, the capacity ofthe pressure chamber of the valve-closing air spring 46 is increased asthe lift position of the valve element 21 moves toward the full-closeposition. Therefore, as shown in FIG. 3, the air pressure within thepressure chamber increases from a minimum pressure P1 at the full-closeposition as the lift position moves toward the valve-opening side, andbecomes a maximum pressure P2 at the full-open position.

[0073] In contrast to the pressure chamber of the valve-closing airspring 46 as mentioned above, the capacity of the pressure chamber ofthe valve-opening air spring 48 is, after being maximized at thefull-open position, reduced as the lift position of the valve element 21moves toward the full-close position. Therefore, the air pressure withinthe pressure chamber of the valve-opening air spring 48 is increasedfrom a minimum pressure P1 at the full-open position as the liftposition moves toward the valve-closing side, and becomes a maximumpressure P2 at the full-close position.

[0074] Accordingly, as shown in FIG. 2a, at the full-open position,since the air pressure within the pressure chamber of the valve-closingair spring 46 becomes the maximum pressure P2, whereas the air pressurewithin the pressure chamber of the valve-opening air spring 48 becomesthe minimum pressure P1, the valve element 21 is energized toward thevalve-closing side by the elastic force of both air springs 46 and 48(Fcl>Fop). On the other hand, at the full-close position, the airpressure within the pressure chamber of the valve-opening air spring 48becomes the maximum pressure P2, whereas the air pressure within thepressure chamber of the valve-closing air spring 46 becomes the minimumpressure P1, as shown in FIG. 2c. Therefore, the valve element 21 isenergized toward the valve-opening side by the elastic force of both airsprings 46 and 48 (Fop>Fcl).

[0075] In addition, the air pressure within each pressure chamber whenthe capacity thereof is at its maximum, that is, the minimum pressure P1is sufficiently higher than an atmospheric pressure P0. In order tosecure the minimum pressure P1, a pressure of the compressed air withinthe reservoir tank 62 is set to the minimum pressure P1.

[0076] Next, a description will be given of an operation mode of theelectromagnetic valve 20 during normal valve opening and closingoperation, In a state where the valve element 21 is placed at thefull-close position, the valve element 21 is, as described above,energized toward the valve-opening side by the resultant force of theelastic forces of the valve-closing air spring 46 and the valve-openingair spring 48. The valve element 21 is held at the full-close positionby supplying a holding current to the electromagnetic coil 34 of thevalve-closing electromagnet 35 to generate an electromagnetic forcewhich attracts and holds the armature 24 to the upper core 32. In thiscase, the magnitude of holding current supplied to the electromagneticcoil 34 is set so as to maintain the state in which the armature 24 isattracted to the upper core 32 against the resultant force of theelastic forces of the valve-closing air spring 46 and the valve-openingair spring 48.

[0077] Next, to operate the valve element 21 maintained at thefull-close position to open toward the full-open position, supply ofholding current to the electromagnetic coil 34 is stopped. As a result,as shown in FIG. 4, the armature 24 is released from the upper core 32,and the valve element 21 is displaced from the full-close positiontoward the valve-opening side by the resultant force of thevalve-closing air spring 46 and the valve-opening air spring 48 thatacts toward the valve-opening side.

[0078] Thereafter, in accordance with the displacement of the valveelement 21 toward the valve-opening side, the resultant force of theelastic forces of the valve-closing air spring 46 and the valve-openingair spring 48 decreases. When the valve element 21 is displaced beyondthe neutral position to the valve-opening side, the resultant force ofthe elastic forces starts to act in a direction to pull the valveelement 21 back. However, the valve element 21 continues to move furthertoward the valve-opening side, to some extent by its own inertia force,against the resultant force of the elastic forces.

[0079] Then, when the valve element 21 reaches a predetermined position,an attracting current is supplied to the electromagnetic coil 38 of thevalve-opening electromagnet 39. An electromagnetic force generated inthe valve-opening electromagnet 39 due to the supply of the attractingcurrent attracts the armature 24 toward the lower core 36. Accordingly,the valve element 21 continues to move, by its own inertia force and theelectromagnetic force of the electromagnet 39, toward the valve-openingside against the resultant force of the elastic forces the valve-closingair spring 46 and the valve-opening air spring 48. In this case, themagnitude of the attracting current is set, for example, according tothe lift position of the valve element 21 or the like that is detectedby the displacement sensor 70, so that the armature 24 is certainlyattracted to the lower core 36.

[0080] Accordingly, as shown in FIG. 5, as the armature 24 is attractedto the lower core 36 and the valve element 21 reaches the full-openposition, a holding current is supplied to the electromagnetic coil 38of the valve-opening electromagnet 39. The electromagnetic forcegenerated thereby attracts and holds the armature 24 to the lower core36.

[0081] Also, to operate the valve element 21, which is maintained at thefull-open position, to close toward the full-close position, as in thesame manner as the opening operation of the valve element 21 from thefull-close position to the full-open position as described above, powersupply to the valve-closing electromagnet 35 and the valve-openingelectromagnet 39 is controlled. That is, by stopping the supply ofholding current to the electromagnetic coil 38 of the valve-openingelectromagnet 39, the valve element 21 starts to move toward thevalve-closing side, and by supplying the attracting current to theelectromagnetic coil 34 of the valve-closing electromagnet 35, thearmature 24 is attracted to the upper core 32.

[0082] After the valve element 21 reaches the full-close position,opening and closing operation of the electromagnetic valve 20 iscontinued by sequentially repeating the aforementioned current supplycontrol. The above are the descriptions of the operation mode of theelectromagnetic valve 20 during normal valve opening and closingoperation.

[0083] Meanwhile, even after the valve element 21 is seated on the valveseat 13, the armature 24 is attracted to the valve-closing electromagnet35 and is displaced toward the valve-closing electromagnet 35 side. Suchdisplacement continues until the armature 24 contacts the valve-closingelectromagnet 35. However, since the armature shaft 23 separates formthe valve shaft 22 after the valve element 21 is seated on the valveseat 13, the armature 24 is not applied with the energizing force by thevalve-closing air spring 46. At this time, to displace the armature 24toward the valve closing side against the energizing force of thevalve-opening air spring 48 toward the valve-opening side, the amount ofcurrent supplied to the valve-closing electromagnet 35 is increased,thereby causing the inconvenience such as increasing power consumption,as mentioned earlier.

[0084] Therefore, in this exemplary embodiment, a pressure within thepressure chamber of the valve-closing air spring 46 is increasedimmediately before the valve element 21 is seated. In other words, thepressure within the pressure chamber of the valve-closing air spring 46is increased during a predetermined period immediately before thearmature shaft 23 starts separate from the valve shaft 22 to move towardthe valve-closing electromagnet 35 side upon seating of the valveelement 21 on the valve seat 13.

[0085] Accordingly, compared to a case in which the pressure is notincreased as described above, the energizing force for energizing thearmature 24 toward the valve-opening side by the resultant force of theelastic forces the valve-closing air spring 46 and the valve-opening airspring 48 is reduced. In other words, an increase, involved withdisplacement of the valve element 21 toward the valve-closing side, inthe energizing force toward the valve-opening side that is applied tothe valve element 21 by the valve-opening air spring 48 and thevalve-closing air spring 46 in accordance with such displacement, is atleast suppressed immediately before the valve element 21 is seated.

[0086] As a result, the degree of decrease in the inertia force of thearmature 24 due to the energizing force for energizing the armature 24toward the valve-opening side by the resultant force of thevalve-closing air spring 46 and the valve-opening air spring 48 is atleast reduced immediately before the valve element 21 is seated.Consequently, the armature 24 can appropriately be attracted to bebrought into contact with the valve-closing electromagnet 35 withoutincreasing the energizing force of the valve-closing electromagnet 35for energizing the armature 24 toward the valve-closing side.

[0087] Furthermore, if the amount of increase in the pressure within thepressure chamber of the valve-closing air spring 46 immediately beforeseating of the valve element 21 is large, the inertia force of thearmature 24 is also increased. In other words, displacement of thearmature 24 toward the valve-closing electromagnet 35 side is alsoaccelerated.

[0088] More specifically, in order to execute such control as mentionedabove, in this exemplary embodiment, as shown in FIG. 1, a high-pressurereservoir tank 80 which accumulates compressed air with a pressure (Px)higher than a pressure (P1) of compressed air accumulated in thereservoir tank 62 is provided. The high-pressure reservoir tank 80 alsoaccumulates the compressed air supplied from the air pump 60. Moreover,a pressure of the compressed air accumulated in the high-pressurereservoir tank 80 is also maintained constant by a regulator or the like(not shown). However, the throttle 61 is not provided between the airpump 60 and the high-pressure reservoir tank 80, thereby making iteasier to accumulate, in the high-pressure reservoir tank 80, thecompressed air with a pressure higher than the pressure of thecompressed air accumulated in the reservoir tank 62.

[0089] The high-pressure reservoir tank 80 is connected to the pressurechamber of the valve-closing air spring 46 through a supply passage 81.Furthermore, a switching valve 82 is provided in the supply valve 63 inorder to selectively supply the pressure chamber of the valve-closingair spring 46 with the compressed air in the high-pressure reservoirtank 80 and that in the reservoir tank 62. The switching valve 82switches, based on a command from the electronic control unit 71,between communication between the upstream and downstream of the supplypassage 63 and that between the supply passage 81 and the downstream ofthe supply passage 63. In other words, the switching valve 82 switchesbetween communication between the reservoir tank 62 and the pressurechamber of the valve-closing air spring 46 via the non-return valve 65,and that between the high-pressure reservoir tank 80 and the pressurechamber of the valve-closing air spring 46 via the non-return valve 65.

[0090] Furthermore, the switching valve 82 is switched so as to increasethe pressure within the pressure chamber of the valve-closing air spring46 immediately before the valve element 21 is seated on the valve seat13. That is, as shown in FIG. 6, the switching valve 82 is switched soas to supply the compressed air accumulated in the high-pressurereservoir tank 80 to the pressure chamber of the valve-closing airspring 46. Accordingly, the non-return valve 65 is closed and thecompressed air accumulated in the high-pressure reservoir tank 80 flowsinto the pressure chamber of the valve-closing air spring 46. As aresult, the pressure within the pressure chamber of the valve-closingair spring 46 immediately before the valve element 21 is seated on thevalve seat 13 can be increased compared to that theretofore. In thiscase, when the compressed air accumulated in the high-pressure reservoirtank 80 is supplied to the pressure chamber of the valve-closing airspring 46, a control such as forcibly closing the relief valve 67 isexecuted.

[0091] By supplying the compressed air accumulated in the high-pressurereservoir tank 80 as mentioned above, as shown in FIG. 7a, the pressurewithin the pressure chamber of the valve-closing air spring 46 isforcibly increased during displacement of the valve element 21 towardthe valve-closing side from a predetermined displacement x0 in thevicinity of the full-close position. Before the predetermineddisplacement x0, the valve element 21 is energized toward thevalve-opening side by the resultant force of the elastic forces of thevalve-opening air spring 48 and the valve-closing air spring 46. Thisenergizing force increases in accordance with displacement of the valveelement 21 toward the valve-closing side as shown in FIG. 7b. After thepredetermined displacement x0 in the vicinity of the full-closeposition, however, since the pressure within the pressure chamber of thevalve-closing air spring 46 is forcibly increased, the actual energizingforce mentioned above is suppressed in relation to the degree ofincrease in the energizing force indicated by a dotted line in FIG. 7b.That is, in this case, the resultant force of the elastic forces of thevalve-opening air spring 48 and the valve-closing air spring 46 becomes,for example, a resultant force f1. Consequently, the degree of decreasein the inertia force of the armature 24 due to the energizing force forenergizing the armature 24 toward the valve-opening side by theresultant force of the elastic forces of the valve-opening air spring 48and the valve-closing air spring 46 is reduced.

[0092] Furthermore, when the degree of forced increase in the pressurewithin the pressure chamber of the valve-closing air spring 46 is high,and the pressure within the pressure chamber of the valve-closing airspring 46 exceeds the pressure within the pressure chamber of thevalve-opening air spring 48, the resultant force of the valve-closingair spring 46 and the valve-opening air spring 48 is directed toward thevalve-closing direction as indicated by a resultant force f2 in FIG. 7b.In this case, displacement of the armature 24 toward the valve-closingside is also accelerated. Accordingly, the inertia force in accordancewith displacement of the armature 24 toward the valve-closing side isincreased.

[0093] By forcibly increasing the pressure within the pressure chamberof the valve-closing air spring 46, the armature 24 can be brought intocontact with the valve-closing electromagnet 35 as shown in FIG. 8.

[0094] According to the exemplary embodiment as described above, thefollowing effects can be obtained.

[0095] (1) A pressure within the pressure chamber of the valve-closingair spring 46 is forcibly increased immediately before the valve element21 is seated. Consequently, the degree of decrease in the inertia forceof the armature 24 due to the energizing force for energizing thearmature 24 toward the valve-opening side by the resultant force of thevalve-closing air spring 46 and the valve-opening air spring 48 can besufficiently reduced immediately before the valve element 21 is seated.Furthermore, if the amount of increase in the pressure within thepressure chamber of the valve-closing air spring 46 immediately beforeseating of the valve element is large, the inertia force of the armaturecan also be increased. In other words, displacement of the armature 24toward the valve-closing electromagnet 35 side is also accelerated. As aresult, the armature 24 can certainly be attracted to and brought intocontact with the valve-closing electromagnet 35.

[0096] (2) As reservoir tanks for supplying compressed air to thepressure chambers of the valve-closing air spring 46 and thevalve-opening air spring 48, the reservoir tank 62 and the high-pressurereservoir tank 80 which accumulates compressed air with a pressurehigher than that of the reservoir tank 62 are provided. Accordingly, thepressure within the pressure chamber of the valve-closing air spring 46can forcibly increased immediately before seating of the valve element21 in a suitable manner.

[0097] (Second Exemplary Embodiment)

[0098] A second exemplary embodiment of a control apparatus of anelectromagnetic valve according to the invention will be describedhereinafter with reference to the accompanying drawings, with a focusdirected on differences from the first exemplary embodiment.

[0099] In the first exemplary embodiment, the pressure within thepressure chamber of the valve-closing air spring 46 is forciblyincreased immediately before the valve element 21 is seated on the valveseat 13. To the contrary, in the second exemplary embodiment, thepressure within the pressure chamber of the valve-opening air spring 48is reduced immediately before the valve element 21 is seated. Therefore,compared to a case in which the pressure is not forcibly reduced asdescried above, the energizing force for energizing the armature 24toward the valve-opening side by the resultant force of thevalve-closing air spring 46 and the valve-opening air spring 48 isreduced. As a result, the degree of decrease in the inertia force of thearmature 24 due to the energizing force for energizing the armature 24toward the valve-opening side by the resultant force of a pair of springmeans is reduced immediately before the valve element 21 is seated.Furthermore, if the amount of the aforementioned pressure reduction islarge, the inertia force in accordance with the displacement of thearmature 24 toward the valve-closing side is increased. Accordingly, thearmature 24 can certainly be attracted to and brought into contact withthe valve-closing electromagnet 35 without increasing the energizingforce of the valve-closing electromagnet 35 that energizes the armature24 toward the valve-opening side.

[0100] More specifically, according to this exemplary embodiment, in astructure as shown in FIG. 9, the relief valve 68 is opened by apredetermined degree so as to reduce the pressure within the pressurechamber of the valve-opening air spring 48 immediately before the valveelement 21 is seated. Consequently, the armature 24 can be brought intocontact with the valve-closing electromagnet 35 just like in the case ofthe first exemplary embodiment.

[0101] According to the aforementioned exemplary embodiment, thefollowing effects can be obtained.

[0102] (3) A pressure within the pressure chamber of the valve-openingair spring 48 is forcibly reduced immediately before the valve element21 is seated. Accordingly, the degree of decrease in the inertia forceof the armature 24 due to the energizing force for energizing thearmature 24 toward the valve-opening side by the resultant force of thevalve-closing air spring 46 and the valve-opening air spring 48 can besufficiently reduced immediately before the valve element 21 is seated.Furthermore, if the amount of decrease in the pressure within thepressure chamber of the valve-opening air spring 48 immediately beforeseating of the valve element is large, the inertia force of the armature24 can also be increased. In other words, displacement of the armature24 toward the valve-closing electromagnet 35 side is also accelerated.As a result, the armature 24 can certainly be attracted to and broughtinto contact with the valve-closing electromagnet 35.

[0103] Each exemplary embodiment described above may be modified asfollows.

[0104] The invention is not limited to the control by which the pressurewithin the pressure chamber of the valve-closing air spring 46 isforcibly increased immediately before the valve element 21 is seated, asdescribed in the first exemplary embodiment. Any control will do as longas the degree of decrease in the pressure within the pressure chamber ofthe valve-closing air spring 46 involved with displacement of the valveelement 21 toward the valve-closing side is forcibly reduced immediatelybefore the valve element 21 is seated. That is, for example, thepressure may assume a larger value than the pressure within the pressurechamber of the valve-opening air spring represented by a curve in FIG.3, so as to reduce the degree of decrease in the pressure within thepressure chamber involved with displacement of the valve element towardthe valve-closing side.

[0105] In this case, control means for forcibly reducing, immediatelybefore the valve element 21 is seated on the valve seat 13, the degreeof decrease in the pressure within the pressure chamber of thevalve-closing air spring 46 involved with displacement of the valveelement 21 toward the valve-opening side, may be configured to includethe high-pressure reservoir tank 80, the relief valve 67, and theelectronic control unit 71. Furthermore, this control means may beprovided with, in place of the non-return valve 65, for example, apressure controller or the like which regulates a pressure of compressedair supplied to the pressure chamber of the valve-closing air spring 46.In this case, by increasing by the pressure controller the pressure ofthe compressed air supplied to the pressure chamber, the degree ofdecrease in the pressure within the pressure chamber immediately beforeseating of the valve element is reduced.

[0106] The invention is not limited to the control by which the pressurewithin the pressure chamber of the valve-opening air spring 48 isforcibly reduced immediately before the valve element 21 is seated, asdescribed in the second exemplary embodiment. Any control will do aslong as the degree of increase in the pressure within the pressurechamber of the valve-opening air spring 48 involved with displacement ofthe valve element 21 toward the valve-closing side is forcibly reducedimmediately before the valve element 21 is seated. That is, for example,the pressure may assume a smaller value than the pressure within thepressure chamber of the valve-opening air spring represented by a curvein FIG. 3, so as to reduce the degree of increase in the pressure withinthe pressure chamber involved with displacement of the valve elementtoward the valve-closing side.

[0107] In this case, control means for forcibly reducing, immediatelybefore the valve element 21 is seated on the valve seat 13, the degreeof increase in the pressure within the pressure chamber of thevalve-opening air spring 48 involved with displacement of the valveelement 21 toward the valve-closing side, may be configured to include,for example, the relief valve 68 and the electronic control unit 71.

[0108] The control means for increasing the pressure within the pressurechamber of the valve-closing air spring 46 immediately before the valveelement 21 is seated on the valve seat 13 is not limited thoseconfigured to include the high-pressure reservoir tank 80, the reliefvalve 67, and the electronic control unit 71. For example, this controlmeans may be provided with, in place of the non-return valve 65, apressure controller or the like which regulates a pressure of compressedair supplied to the pressure chamber of the valve-closing air spring 46.In this case, by increasing by the pressure controller the pressure ofthe compressed air supplied to the pressure chamber, the pressure withinthe pressure chamber is increased immediately before seating of thevalve element.

[0109] The control means for reducing, immediately before the valveelement 21 is seated on the valve seat 13, the pressure within thepressure chamber of the valve-opening air spring 48 in accordance withdisplacement of the valve element 21 toward the valve-closing side, isnot limited to those configured to include the relief valve 68 and theelectronic control unit 71.

[0110] The structure of the air pressure circuit, the arrangement of theair springs 46 and 48 in the electromagnetic valve 20, the structure ofthe control system, and the like according to the aforementionedexemplary embodiments may be arbitrarily changed.

[0111] In the exemplary embodiments above, an air spring that generatesan elastic force by the pressure of the compressed air filled in thepressure chamber is adopted as a spring for energizing the valve element21 toward the displacement ends on the valve-opening side andvalve-closing side. However, any gas other than the atmospheric air mayalso be used as a source for generating the elastic force.

[0112] Furthermore, spring means other than a pneumatic spring may beadopted as long as the energizing force can be arbitrarily changed.

[0113] While the invention has been described with reference toexemplary embodiments thereof, it is to be understood that the inventionis not limited to the exemplary embodiments or constructions. To thecontrary, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of theexemplary embodiments are shown in various combinations andconfigurations, which are exemplary, other combinations andconfigurations, including more, less or only a single element, are alsowithin the spirit and scope of the invention.

What is claimed is:
 1. A control apparatus of an electromagnetic valvewhich includes a valve element, an armature connected to an armatureshaft which is engaged with the valve element, a pair of spring meansfor energizing the valve element toward a valve-opening side and avalve-closing side, respectively, and an electromagnet for energizingthe armature toward the valve-closing side of the valve element, andoperates the valve element to open and close by cooperative operation ofan electromagnetic force of the electromagnet and an energizing force ofthe spring means, comprising: a controller which increases, immediatelybefore seating of the valve element, the energizing force of the springmeans for energizing the valve-element toward the valve-closing side. 2.The control apparatus of the electromagnetic valve according to claim 1,wherein at least one of the pair of the spring means is configured as avalve-closing pneumatic spring, wherein the valve closing pneumaticspring energizes a piston connected to a valve shaft of the valveelement toward the valve-closing side by a pressure within a pressurechamber of the valve-closing pneumatic spring, and the controller has afunction to control the pressure within the pressure chamber foradjusting an energizing force of the valve-closing pneumatic spring. 3.The control apparatus of the electromagnetic valve according to claim 2,wherein the controller increases the pressure within the pressurechamber of the valve-closing pneumatic spring immediately before seatingof the valve element.
 4. The control apparatus of the electromagneticvalve according to claim 2, wherein the controller forcibly reduces,immediately before seating of the valve element, a degree of decrease inthe pressure within the pressure chamber of the valve-closing pneumaticspring involved with displacement toward the valve-closing side.
 5. Acontrol apparatus of an electromagnetic valve which includes a valveelement, an armature connected to an armature shaft which is engagedwith the valve element, a pair of spring means for energizing the valveelement toward a valve-opening side and a valve-closing side,respectively, and an electromagnet for energizing the armature towardthe valve-closing side of the valve element, and operates the valveelement to open and close by cooperative operation of an electromagneticforce of the electromagnet and an energizing force of the spring means,comprising: a controller which reduces, immediately before seating ofthe valve element, the energizing force of the spring means forenergizing the valve-element toward the valve-opening side.
 6. Thecontrol apparatus of the electromagnetic valve according to claim 5,wherein at least one of the pair of the spring means is configured as avalve-opening pneumatic spring, wherein the valve-opening pneumaticspring energizes a piston connected to a valve shaft of the valveelement toward the valve-opening side by a pressure within a pressurechamber of the valve-opening pneumatic spring, and the controller has afunction to control the pressure within the pressure chamber foradjusting an energizing force of the valve-opening pneumatic spring. 7.The control apparatus of the electromagnetic valve according to claim 6,wherein the controller reduces the pressure within the pressure chamberof the valve-opening pneumatic spring immediately before seating of thevalve element.
 8. The control apparatus of the electromagnetic valveaccording to claim 6, wherein the controller forcibly reduces,immediately before seating of the valve element, a degree of increase inthe pressure within the pressure chamber of the valve-opening pneumaticspring involved with displacement toward the valve-closing side.
 9. Acontrol apparatus of an electromagnetic valve which includes a valveelement, an armature connected to an armature shaft which is engagedwith the valve element, a valve-opening pneumatic spring for energizingthe valve element toward a valve-opening side, a valve-closing pneumaticspring for energizing the valve element toward a valve-closing side, anda pair of electromagnets for energizing the armature in both axialdirections of the armature shaft, respectively, and operates the valveelement to open and close by cooperative operation of an electromagneticforce of each electromagnet and an energizing force of each pneumaticspring, comprising: a controller which forcibly reduces, immediatelybefore seating of the valve element, a degree of increase in theenergizing force by which the valve-opening pneumatic spring and thevalve-closing pneumatic spring energize the valve element toward thevalve-opening side in accordance with displacement of the valve elementtoward the valve-closing side.
 10. A control method of a controlapparatus of an electromagnetic valve which includes a valve element, anarmature connected to an armature shaft which is engaged with the valveelement, a pair of spring means for energizing the valve element towarda valve-opening side and a valve-closing side, respectively, and anelectromagnet for energizing the armature toward the valve-closing sideof the valve element, and operates the valve element to open and closeby cooperative operation of an electromagnetic force of theelectromagnet and an energizing force of the spring means, comprisingthe following steps of: supplying an electric current to theelectromagnet so as to energize the valve element toward thevalve-closing side; and increasing, immediately before seating of thevalve element, the energizing force of the spring means for energizingthe valve element toward the valve-closing side.
 11. The control methodaccording to claim 10, wherein at least one of the pair of the springmeans is configured as a valve-closing pneumatic spring, wherein thevalve-closing pneumatic spring energizes a piston connected to a valveshaft of the valve element toward the valve-closing side by a pressurewithin a pressure chamber of the valve-closing pneumatic spring, and thepressure within a pressure chamber of the valve-closing pneumatic springis increased immediately before seating of the valve element.
 12. Thecontrol method according to claim 10, wherein a degree of decrease inthe pressure within the pressure chamber of the valve-closing pneumaticspring involved with displacement toward the valve-closing side isforcibly reduced immediately before seating of the valve element.
 13. Acontrol method of a control apparatus of an electromagnetic valve whichincludes a valve element, an armature connected to an armature shaftwhich is engaged with the valve element, a pair of spring means forenergizing the valve element toward a valve-opening side and avalve-closing side, respectively, and an electromagnet for energizingthe armature toward the valve-closing side of the valve element, andoperates the valve element to open and close by cooperative operation ofan electromagnetic force of the electromagnet and an energizing force ofthe spring means, comprising the following steps of: supplying anelectric current to the electromagnet so as to energize the valveelement toward the valve-closing side; and reducing, immediately beforeseating of the valve element, the energizing force of the spring meansfor energizing the valve element toward the valve-opening side.
 14. Thecontrol method according to claim 13, wherein at least one of the pairof the spring means is configured as a valve-opening pneumatic spring,wherein the valve-opening pneumatic spring energizes a piston connectedto a valve shaft of the valve element toward the valve-opening side by apressure within a pressure chamber of the valve-opening pneumaticspring, and a pressure within a pressure chamber of a valve-openingpneumatic spring is reduced immediately before seating of the valveelement.
 15. The control method according to claim 13, wherein a degreeof increase in the pressure within the pressure chamber of thevalve-opening pneumatic spring involved with displacement toward thevalve-closing side is forcibly reduced immediately before seating of thevalve element.
 16. A control method of a control apparatus of anelectromagnetic valve which includes a valve element, an armatureconnected to an armature shaft which is engaged with the valve element,a valve-opening pneumatic spring for energizing the valve element towarda valve-opening side, a valve-closing pneumatic spring for energizingthe valve element toward a valve-closing side, and a pair ofelectromagnets for energizing the armature in both axial directions ofthe armature shaft, respectively, and operates the valve element to openand close by cooperative operation of an electromagnetic force of eachelectromagnet and an energizing force of each pneumatic spring,comprising the following steps of: supplying an electric current to theelectromagnet so as to energize the valve element toward thevalve-closing side; and forcibly reducing, immediately before seating ofthe valve element, a degree of increase in the energizing force by whichthe valve-opening pneumatic spring and the valve-closing pneumaticspring energize the valve element toward the valve-opening side inaccordance with displacement of the valve element toward thevalve-closing side.